In a network, impedance change or Return Loss (RL) change of one or more nodes while another node is transmitting or receiving may cause interference. This is because a signal propagating through the network is a composite of all reflections of all nodes. Therefore, if any reflected signal component changes, the composite will also change, affecting reception or transmission. This is shown in FIG. 1, which depicts multiple Customer Premises Equipment (CPEs), or nodes 10, 10′, 10″, in a network (of coaxial cables 16 and taps 15, 15′ and 15″ connecting CPE units and Network Controller (NC 14)). Single port taps are shown for simplicity, but often multiport taps are used in a typical CATV plant showing the effects of adjacent nodes return loss change. As shown in FIG. 1, the signal propagating to network controller (NC) 14 includes direct path data signal 12 and reflections 18 from nodes 10′ and 10″. If the impedance of any of the nodes 10′ or 10″ changes, the reflections will change and consequently the received signal at NC 14 will change. Depending on isolation of nodes and the amount of RL change, the effect can degrade the link, cause packet errors, and in some cases may disable communications.
For the above reasons, as taught in the prior art, all the nodes are always kept in the same state (in the transmit mode with unchanged output impedance) all the time, no matter if they are actively transmitting or not. When not transmitting any data or intended content, but ready to transmit data at any moment, this is referred to as a “transmit-ready” or “mute” state.
However, aggregate noise power of all the mute nodes while another node is transmitting will degrade the sensitivity of the receiver or NC 14 to the actively transmitting node. Alternatively, in the prior art an opposite choice is made by turning the transmitters off, so that noise is eliminated, but at the expense of significant impedance/return loss changes, and increased delay in turning the transmitters back on.
Clearly, achieving both low noise and unchanged impedance is advantageous, and that is the objective of the claimed embodiments.